A Wireless, Magnetoelastic-Based Sensor Array for Force Monitoring on a Hard Surface

A force monitoring system consisting of stress-sensitive magnetoelastic strips for remotely measuring the force profile across a hard surface is described. Under the excitation of a magnetic AC field, the magnetoelastic strips generated higher-order harmonic fields (magnetic AC fields at multiple frequencies of the excitation field), allowing remote measurement of their responses without interference from the excitation field. Due to their magnetoelastic properties, these higher-order harmonic fields were also dependent on the applied force and, as a result, variations in force/stress could be tracked via changes in the field amplitudes. These changes were monitored using a detection system featuring a set of magnetic detection coils, which captured the response of the magnetoelastic strips. To demonstrate the functionality of this sensor system, a three-strip magnetoelastic sensor array was fabricated on a flat polycarbonate substrate. The substrate, placed within a customized mechanical loader, was exposed to a variety of force loading conditions. Experimental results demonstrated a proportional relationship between the amplitude of the 2nd order harmonic field and the applied force. An algorithm was developed to identify the magnitude of the applied force. The novelty of this system lies in its wireless and passive nature, which is ideal for applications in which wires and internal power sources are prohibited or discouraged. Moreover, the sensing component of this system is an array of thin magnetoelastic strips, allowing for minimal modifications to existing structures during implementation.